This invention relates to a distributed generation system for stabilizing a power system by suppressing the voltage fluctuation in the power system and a method of stabilizing the power system.
In a power distribution system with which a distributed generation such as a wind turbine is connected, it is generally necessary to suppress the voltage fluctuation caused in the power distribution system due to the fluctuations in the output of a distributed generation or in a load connected with the power distribution system.
JP-A-2000-333373 discloses a method of compensating the fluctuations in the system voltage by a distributed generation connected with the system. Namely, in this patent document, there is disclosed a method wherein the system voltage and the system current are detected; the reactive current command for the distributed generation is generated on the basis of the detected system voltage and current; and the voltage on the distributed line is maintained constant with the aid of the reactive current command.
Further, JP-A-2002-171667 discloses a system stabilizing technique for suppressing the fluctuations in the voltage of a power distribution system by the use of a static var compensator incorporating IGBTs therein. According to this patent document, the distributed generation connected via a system interconnection line with a trunk system generates active power P and reactive power Q and feed them to the trunk system. Between the trunk system and the distributed generation is connected a self-commutated static var compensator using, for example, IGBTs. The current flowing from the distributed generation to the interconnection line is detected and the voltage is detected at the point of connection between the trunk system and the distributed generation. As a result, the active power P supplied from the distributed generation to the trunk system is detected. Finally, the IGBTs in the self-commutated static var compensator are controlled in such a manner that the fluctuation in the amplitude of the voltage at the point of connection is suppressed. More specifically, the static var compensator produces reactive power Qc such that Qc=−[Q+(R/X)P], where R and X indicate the resistive and reactance components of the impedance of the interconnection line, respectively. They may change depending on the service condition of the interconnection line. Hence, the static var compensator calculates the parameter (R/X) by measuring the interharmonic current resulting from the insertion of an interharmonic voltage.